Method of making an infrared reflective glass sheet-II

ABSTRACT

This disclosure is directed to a method of making an infrared reflective glass sheet. The method has the following steps. The glass sheet formed of soda/lime silica glass is selected. The glass sheet is heated to a temperature in a range from 900° to 1100° F. If desired, the sheet glass selected may be selected at the time it is being manufactured in a glass manufacturing operation and it would have upon leaving a process such as a float process a temperature in a range of 900° to 1100° F. An organic/tin ion-containing, chlorine-free compound is applied to a surface of the glass sheet. Application of this compound forms a tin oxide seal coating having a columnar grain microstructure on the surface of the glass sheet. A coating of tin oxide is applied to the tin oxide seal coating. The coating of tin oxide is formed from the decomposition of butyltin trichloride. The columnar growth of the tin oxide seal coating is continued by a columnar growth in the tin oxide coating without any physical distinguishing microstructure characteristics between the tin oxide of each section of growth. The glass sheet is cooled to room temperature after application of the tin oxide seal coating and the tin oxide coating thereon.

TECHNICAL FIELD

This application is directed to a method of making an infraredreflective glass sheet. The glass sheet so made may be used as a windowin a building, the window being one which reflects infrared radiation.Utilization of such a window can reduce the amount of heat lost from theinterior of the building containing the window because the window iseffective in preventing the loss of infrared radiation from the interiorof the building.

BACKGROUND AND PRIOR ART STATEMENT

The manufacture of glass windows coated with infrared radiationreflective films is known in the art, see U.S. Pat. No. 4,440,822,issued Apr. 3, 1984, entitled "Non-Iridescent Glass Structures". Thepurpose of placing such a coating on a glass is that the coating iseffective in reflecting radiation in the infrared band. This radiationis heat radiation and if it is trapped within a building by the glassstructure, the building requires less total energy to keep it heated toa particular temperature.

We are also aware of U.S. Pat. No. 4,144,362, issued Mar. 13, 1979, for"Method for Coating Glass Using Monoalkyltin Trihalides". This patentdiscloses a method for obtaining a stannic oxide coating on a glasssurface by applying an organotin compound to a heated glass surface. Thepurpose of coating the glass was to improve the impact and abrasionresistance of the glass. This patent disclosed that a butyltintrichloride could be pyrolized to provide an acceptable stannic oxidecoating on heated glass surfaces. As described in the patent, thestannic oxide coating in combination with a synthetic polymer coating atthe cold end of the annealing lehr improved the scratch resistance ofthe glass article. In particular, the patent also indicated that thecontainers coated with this material exhibited a higher burst strengththan containers coated using other prior art organotin compounds such asdimethyltin dichloride. Once again, the aforementioned '362 patent isdevoid of mentioning the utilization of the butyltin trichloride inorder to make infrared reflective glass sheets, and does not mentiondoping the film with fluoride ions.

In our opinion, it is desirable to form an infrared reflective film on aglass surface using butyltin trichloride because this material hasseveral advantages. These advantages are:

1. The utilization of butyltin trichloride results in the application ofa very smooth film on a glass surface. A smooth film is desirablebecause it reduces the variation in reflected color and improves theoverall reflective color appearance, gives less film reflected color"texture" or "mottle" and gives a smoother reflective color variationacross a glass sample than other organotin compounds such as dibutyltindiacetate (DBDA) or dibutyltin difluoride (DBDF).

2. Butyltin trichloride, especially n-butyltin trichloride (NBTC) isvery soluble in a water-miscible solvent such as methanol. This allows awide range of organotin compound concentration solutions to be used aswell as allowing doping with water soluble fluoride compounds such asammonium fluoride. The high concentrations of butyltin trichloridepossible allows rapid formation of relatively thick films (150 to 1000nanometers) at high volume glass throughout with minimum cooling of theglass substrate due to solvent evaporation and limited spray zonelength.

3. Butyltin trichloride does not hydrolyze in water like most inorganictin chlorides, therefore allowing the use of water soluble fluoridessuch as ammonium fluoride as the fluoride dopant.

4. Butyltin trichloride allows formation of good infrared reflectingfilms without the use of organic solvents. This eliminates the need forcostly hydrocarbon emission control equipment and the use of flammableor toxic solutions.

5. The combination of lower organic content and presence of chlorine inthe butyltin trichloride solutions doped with fluorine improves theelectroconductivity and infrared reflectance of the resulting film overother organotin compounds. The butyltin trichloride-induced film has agrain structure which gives improved electroconductivity.

6. The relatively high vapor pressure of butyltin trichloride at roomtemperature allows spraying on the glass ribbon with less cooling thanmost tin compounds. This high vapor pressure also allows vapor as wellas solution spraying to form the films. In vapor spraying, the butyltintrichloride can be doped with fluorine-containing compounds such as1,1,2, trichloro-1,1,2, trifluoroethane to obtain the proper level offluoride doping.

7. The amount of fluoride ion doping in the butyltin trichloridesolutions and the SnO_(x) film to obtain good electroconductivity ismuch less than in other organotin solutions, such as those employingdibutyltin diacetate (DBDA) and dibutyltin difluoride (DBDF). Thisresults in less fluoride emissions.

As an additional matter, when one is dealing with infrared reflectiveglass, very desirable infrared reflective properties may be achieved atrelatively low thicknesses of films from butyltin trichloride ascompared to those from other materials, for example, dibutyltindiacetate doped with fluoride ions. However, we found that when weapplied butyltin trichloride directly to the surface of the glass sheet,there was the undesirable interaction of the chlorine in the spraymaterial and the sodium on the surface of the glass sheet which resultedin the formation of crystals of sodium chloride. Formation of crystalsresulted subsequently in the production of voids in the film and thelight scattering defect known as haze. This haze is unacceptable becauseit is noticeable when looking through the glass.

We found that we could solve the problem of haze production by applyinga seal coating on the surface of the glass sheet prior to theapplication of the coating of tin oxide formed by decomposition ofbutyltin trichloride. The special seal coating leads to formation of atin oxide film on the glass having a columnar grain microstructure thatgives special qualities to the tin oxide film.

No search was conducted on the subject matter of this specification inthe U.S. Patent Office or in any other search facility. We are unawareof any prior art more relevant to the subject matter of thisspecification than that which was set forth hereinabove.

DISCLOSURE OF INVENTION

This invention relates to a method of making an infrared reflectiveglass sheet. In particular, the method of our invention is directed tothe making of an infrared reflective glass sheet, the glass sheet beingeffective to return infrared radiation received from objects placed awayfrom the film side of the glass sheet. In accordance with the teachingsof the method of this invention, an infrared reflective glass sheet ismade in the following way. A glass sheet formed of soda/lime silicaglass is selected. The glass sheet is heated to a temperature in a rangefrom 900° to 1100° F. An organic/tin ion-containing, chlorine-freecompound is applied to a surface of the glass sheet. This action forms atin oxide seal coating on the surface of the glass sheet having acolumnar grain microstructure. Thereafter, a coating of tin oxide formedfrom the decomposition of butyltin trichloride is applied to the tinoxide seal coating on the glass sheet. The columnar growth of the tinoxide seal coating is continued by a columnar growth in the tin oxidecoating. There are no physical distinguishing microstructuralcharacteristics between the tin oxide of each section of growth. Theglass sheet is cooled to room temperature after application of the tinoxide seal coating and tin oxide coating thereon.

In accordance with detailed teachings of the method of our invention,the seal coating may have a thickness in a range from 25 to 100nanometers. The overall thickness of the two coatings combined is in arange from 100 to 400 nanometers.

Many different materials are available to be used as the organic/tinion-containing, chlorine-free compound to form the seal coating. Forexample, dibutyltin diacetate solution doped with fluoride is a materialwhich serves very well in this function. The seal coating produced byapplying this material is a tin oxide doped with fluoride.

When the method of our invention is used to form an infrared reflectiveglass sheet, the final glass sheet has several desirablecharacteristics. For example, its overall reflective color is veryuniform throughout the entire extent of the film. This is particularlyof value in the situation where the film is being manufactured on thefloat glass process. Film uniformity over the entire width of the ribbonallows the cutting of very large glass brackets. The uniformity of thefilm is very high and it therefore has a very desirable texture andlittle if any mottle. Mottle is defined as localized, nonuniform filmthickness that causes a nonuniform reflective color appearance undercertain lighting conditions. As an additional matter, the emissivity ofthe film, which is a measurement of the ability of the film to reflectinfrared radiation, is very good. Normally the emissivity is 0.40 orlower. When the emissivity is in the range of 0.40 or lower, the glasshas very desirable characteristics in that a double-glazed insulatedunit with one pane having said emissivity on an interior surface isroughly equivalent to a triple-glazed insulated unit in thermalperformance. We believe that these characteristics are achieved becausethe film is made up of a columnar grain microstructure in which thecolumnar growth takes place without any physical distinguishingcharacteristics between the tin oxide of each section.

BEST MODE AND INDUSTRIAL APPLICABILITY

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments.

The following description is what we consider to be preferredembodiments of the method of our invention. The following descriptionalso sets forth what we now contemplate to be the best mode of carryingout the method of our invention. The description, however, is notintended to be a limitation upon the broader principles of this method,and while preferred materials are used to illustrate the method of ourinvention in accordance with the requirements of the laws, it does notmean that other materials not mentioned herein cannot be used in themethod.

The method of making an infrared reflective glass sheet in accordancewith the teachings of our invention is initiated as follows. A glasssheet formed of soda/lime silica glass is selected. Soda/lime silicaglass is the common glass manufactured throughout the world for thepurpose of making window structures for buildings, motor vehicles, andmany other applications. Normally, the soda/lime silica glass selectedis one which has a clear body color. That is, the normal colorattributed to soda/lime glass without the addition of coloring agents tosecure a green, bronze, or other body tint thereto. However, theinvention is equally applicable and may be used to place infraredreflective films on a glass even though that glass has a body color, forexample, blue, green, bronze, gray, or any other of the well knowncommercial colors.

As an initial step in the method of our invention, the selected glasssheet is heated to a temperature in a range of 900°-1100° F. Of course,as is readily apparent, the selection and heating of the glass sheet maybe accomplished in a single step, that is, in the manufacturing of theglass sheet in a process such as the float process. In the floatprocess, a continuous sheet of glass is produced. As that glass leavesthe float chamber, as is well known to those skilled in the art, theglass sheet will still be heated to a temperature in the desired range.Thus, the selection of the glass sheet and heating of the glass sheetmay take place as a single step of producing a glass sheet which has atemperature in the desired range, the production taking place, forexample, in a process such as the float process for manufacturing glass.

In accordance with the teachings of the method of our invention, anorganic/tin ion-containing, chlorine-free compound is applied to thesurface of the glass sheet while in its heated condition. Application ofthe organic/tin ion-containing, chlorine-free compound forms a tin oxideseal coating on the surface of the glass sheet. Preferably, theorganic/tin ion-containing, chlorine-free compound is applied to thesurface of the glass sheet in a spraying operation in which the compoundhad been dissolved in a suitable solvent or vapor sprayed.

One material that is usable as the organic/tin ion-containing,chlorine-free compound is dibutyltin diacetate. This material isdissolved in a suitable solvent such as methanol and doped with a watersoluble fluoride compound such as ammonium fluoride. The amount ofdibutyltin diacetate dissolved in the solvent can be from 5 to 100%, buttypically ranges from 20 to 30%. The amount of fluoride added can vary,but best results occur at a 2.0 F/Sn molar ratio with ammonium fluoride(NH₄ F) as the fluoride source. The amount of water added can be up to0.92 wt. % of the ammonium fluoride. This material is sprayed on the hotglass to develop a seal coating having a thickness in a range from about25-100 nanometers. A purpose of the seal coating is that it must bethick enough to block out any interaction between a chlorine-containingmaterial and sodium on the glass surface. When this material is used asthe seal coating, the coating composition formed is a tin oxide coating.With this tin oxide coating being electroconductive, the infraredreflectance is improved for a given total film thickness. As theelectroconductivity of the sealant film improves, theelectroconductivity of the two-solution sample approaches that of asample of the pure overcoat of the same thickness. The tin oxide sealcoating has a columnar grain microstructure. In particular, the sealcoating is made up of a plurality of grains, each of which grows as acolumn up from the surface of the glass sheet.

Many other seal coating materials may be used. The only characteristicsthat are required are that the seal coating be an organic/tinion-containing, chlorine-free compound which when applied to heatedglass will react therewith in order to form a tin oxide seal coating onthe surface of the glass sheet which has a columnar grainmicrostructure. The seal coating must be one which will not allowpenetration thereof by chlorine-containing materials which would then bein a position to react with sodium on the surface of the glass to formcrystals of sodium chloride. As discussed in earlier portions of thisspecification, the formation of sodium chloride is detrimental becausesuch production produces voids in the film which leads to a conditionknown as haze or light scattering by the so-produced film.

After the tin oxide seal coating has been applied to the glass sheet, acoating of tin oxide doped with fluoride is applied to the tin oxideseal coating. The coating of tin oxide is formed from the decompositionof butyltin trichloride as this material produces a very uniform film ofvery uniform color. The butyltin trichloride may be applied by solutionspraying or vapor spraying. For example, a solution formed of about 50%of the butyltin trichloride with the balance being methanol can besprayed onto the glass sheet after the tin oxide seal coating has beenplaced thereon. One should also include in the spraying composition asmall amount of a fluoride compound such as ammonium fluoride in orderto get the fluoride ion into the tin oxide coating to be formed. Thefluoride ion is effective to increase the IR reflectance of the glassfilm. The amount of fluoride needed is about 0.2 F/Sn molar ratio withan equal weight percent water. The amount of NH₄ or H₂ O may vary. Thepreferred butyltin trichloride compound used is normal butyltintrichloride.

The tin oxide coating from the butyltin trichloride coating is one whichcontinues the columnar growth of the tin oxide seal coating. There areno physical distinguishing microstructure characteristics between thetin oxide of each section of growth.

The method is finished by cooling the glass sheet to room temperatureafter application of the tin oxide seal coating and the tin oxidecoating thereon. The total thickness of these two coatings should be ina range from 100-400 nanometers to get the best characteristics from thefilm.

EXAMPLE 1

Solution A (Sealant Film)

Dibutyltin Diacetate: 20 Wt. %

Ammonium Fluoride: 6.3 Wt. %

Water: 5.8 Wt. %

Methanol: 58.0 Wt. %

Solution B (Overcoat Film)

Butyltin Trichloride: 53.8 Wt. %

Ammonium Fluoride: 1.4 Wt. %

Water: 1.4 Wt. %

Methanol: 43.4 Wt. %

With a flow rate of 0.115 gallons per minute of Solution A and 0.285gallons per minute of Solution B, a film thickness of 180 nanometers isobtained uniformly across the ribbon with an emittance of 0.33 on 1/8inch clear glass with a lehr speed of 250 inches per minute. The filmhas a visible transmittance of 83-85% and is haze-free.

EXAMPLE 2

With flow rates of 0.2 gallons per minute of Solution A and 0.6 gallonsper minute of Solution B, a 400 nanometer film is obtained with anemittance of 0.23. The lehr speed is 250 inches per minute.

EXAMPLE 3

Solution A (Sealant Film)

Same as Example 1.

Solution C

Butyltin Trichloride: 20 Wt. %

Ammonium Fluoride: 0.52 Wt. %

Water: 0.52 Wt. %

Methanol: 79 Wt. %

With flow rates of 0.115 gallons per minute of Solution A and 0.6gallons per minute of Solution C, a film thickness of about 180nanometers with an emittance of 0.38 is obtained on 1/8 inch clear glasswith a lehr speed of 250 inches per minute.

EXAMPLE 4

Solution D

Butyltin Trichloride: 68.7 Wt. %

Ammonium Fluoride: 1.9 Wt. %

Water: 1.9 Wt. %

Methanol: 27.5 Wt %

With flow rates of 0.19 gallons per minute of Solution A and 0.56gallons per minute of Solution D, a film thickness of about 408nanometers with an emittance of 0.27 is obtained at a lehr speed of 231inches per minute.

EXAMPLE 5

With flow rates of 0.12 gallons per minute of Solution A and 0.33gallons per minute of Solution D, a film thickness of 200 nanometerswith an emittance of 0.33 is obtained at a lehr speed of 231 inches perminute.

EXAMPLE 6

Solution E

Butyltin Trichloride: 77 Wt. %

Ammonium Fluoride: 2.0 Wt. %

Water: 21.0 Wt. % .

With flow rates of 0.12 gallons per minute of Solution A and 0.34gallons per minute of Solution E, a film thickness of 201 nanometerswith an emittance of 0.34 is obtained at a lehr speed of 231 inches perminute.

While particular embodiments of the method of our invention have beenillustrated and described, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom the invention, and it is intended to cover in the appended claimsall such modifications and equivalents as fall within the true spiritand scope of this invention.

We claim:
 1. A method of making an infrared reflective glass sheet whichcomprises the steps of:selecting a glass sheet formed of soda/limesilica glass; heating said glass sheet to a temperature in a range from900° to 1100° F.; applying to a surface of said glass sheet anorganic/tin ion-containing, chlorine-free compound to form a tin oxideseal coating having a columnar grain microstructure on said surface ofsaid glass sheet; applying to said tin oxide seal coating a coating oftin oxide formed from the decomposition of butyltin trichloride dcpedwith fluoride, said columnar growth of said tin oxide seal coating beingcontinued by a columnar growth in said tin oxide coating without anyphysical distinguishing microstructure characteristics between the tinoxide of each section of growth; cooling said glass sheet to roomtemperature after application of said tin oxide seal coating and saidtin oxide coating thereon.
 2. A method of making an infrared reflectiveglass sheet which comprising the steps of:forming a glass sheet ofsoda/lime silica glass at a temperature in a range from 900° to 1100°F.; applying to a surface of said glass sheet an organic/tinion-containing, chlorine-free compound to form a tin oxide seal coatinghaving a columnar grain microstructure on said surface of said glasssheet; applying to said tin oxide seal coating a coating of tin oxideformed from the decomposition of butyltin trichloride, said columnargrowth of said tin oxide seal coating being continued by a columnargrowth in said tin oxide coating without any physical distinguishingmicrostructure characteristics between the tin oxide of each section ofgrowth; cooling said glass sheet to room temperature after applicationof said tin oxide seal coating and said tin oxide coating thereon. 3.The method of claim 1, wherein said tin oxide seal coating has athickness in a range of 25-100 nanometers.
 4. The method of claim 3,wherein the combined coating of said tin oxide seal coating and said tinoxide coating have a thickness in a range from 100 to 400 nanometers. 5.The method of claim 2, wherein said tin oxide seal coating has athickness in a range of 25-100 nanometers.
 6. The method of claim 5,wherein the combined coating of said tin oxide seal coating and said tinoxide coating have a thickness in a range from 100 to 400 nanometers.